Spatially unequal streaming

ABSTRACT

Various concepts for media content streaming are described. Some allow for streaming spatial scene content in a spatially unequal manner so that the visible quality for the user is increased, or the processing complexity or used bandwidth at the streaming retrieval site is decreased. Others allow for streaming spatial scene content in a manner enlarging the applicability to further application scenarios.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/819,957, filed Mar. 16, 2020, which is a continuation of U.S. patentapplication Ser. No. 16/381,912, filed Apr. 11, 2019, now U.S. Pat. No.11,218,530, which is a continuation of copending InternationalApplication No. PCT/EP2017/075971, filed Oct. 11, 2017, which isincorporated herein by reference in its entirety, and additionallyclaims priority from European Application No. 16193601.8, filed Oct. 12,2016, and from European Application No. 17180403.2, filed Jul. 8, 2017,which are also incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The present application is concerned with spatially unequal streamingsuch as occurring in virtual reality (VR) streaming.

VR streaming typically involves transmission of a very high-resolutionvideo. The resolving capacity of the human fovea is around 60 pixels perdegree. If transmission of the full sphere with 360°×180° is considered,one would end up by sending a resolution of around 22 k×11 k pixels.Since, sending such high resolution would lead to tremendously highbandwidth requirements, another solution is to send only the viewportshown at the Head Mounted Displays (HMDs), which have FoV of 90°×90°:leading to around a 6 k×6 k pixels video. A trade-off between sendingthe whole video at the highest resolution and sending only the viewportis to send the viewport at high resolution and some neighboring data (orthe rest of the spherical video) at lower resolution or lower quality.

In a DASH scenario, an omni-directional video (aka spherical video) canbe offered in such a way that the mixed resolution or mixed qualityvideo described before is controlled by the DASH client. The DASH clientonly needs to know information that describes how the content isoffered.

One example could be to offer different representations with differentprojections that have asymmetric characteristics, such as differentquality and distortion for different parts of the video. Eachrepresentation would correspond to a given viewport and would have theviewport encoded with a higher quality/resolution than the rest of thecontent. Knowing the orientation information (direction of the viewportfor which the content has been encoded with a higher quality/resolution)the DASH client can chose one or another representation dynamically tomatch the viewing direction of the user at any time.

A more flexible option for a DASH client to select such asymmetriccharacteristic for the omni-directional video would be when the video issplit into several spatial regions, with each region being available atdifferent resolution or quality. One option could be to split it intorectangular regions (aka tiles) based on a grid, but other options couldbe foreseen. In such a case, the DASH client would need some signalingabout the different qualities into which the different regions areoffered and it could download the different regions at differentqualities so that the viewport shown to the user is at a better qualitythan the other non-shown content.

In any of the previous cases, when user interaction happens and theviewport is changed, the DASH client will need some time to react touser movement and download the content in such a way that matches thenew viewport. During the time between the user moves and the DASH clientadapts its requests to match the new viewport, the user will see in theviewport some regions in high quality and low quality simultaneously.Though the acceptable quality/resolution difference is contentdependent, the quality the user sees is in any case degraded.

Thus, it would be favorable to have a concept at hand which alleviates,or renders more efficient, or even increases the visible quality for theuser with respect to partial presentation of spatial scene contentstreamed by adaptive streaming.

Thus, the object of the present invention to provide concepts forstreaming spatial scene content in a spatially unequal manner so thatthe visible quality for the user is increased, or the processingcomplexity or used bandwidth at the streaming retrieval site isdecreased, or to provide concepts for streaming spatial scene content ina manner enlarging the applicability to further application scenarios.

SUMMARY

An embodiment may have a video bitstream having a video encodedthereinto, the video bitstream having a signalization of a size and/or aposition of one or more of a focus area within the video onto which adecoding power for decoding the video should be focused, and arecommended advantageous view-section area of the video.

Another embodiment may have a decoder for decoding a video bitstreamhaving a video encoded thereinto, the decoder being configured to derivefrom the video bitstream a signalization of a size and/or position ofone or more of a focus area within the video onto which a decoding powerfor decoding the video should be focused, and a recommended view-sectionarea of the video.

Another embodiment may have a device for streaming a video bitstreamfrom a server, configured to retrieve from the server information on asize and/or a position of one or more of a focus area within the videoonto which a decoding power for decoding the video should be focused,and a recommended view-section area of the video, and use theinformation in adaptively streaming the video bitstream from the server.

Still another embodiment may have a method for decoding a videobitstream having a video encoded thereinto, the decoding beingconfigured to derive from the video bitstream a signalization of a sizeand/or position of one or more of a focus area within the video ontowhich a decoding power for decoding the video should be focused, and arecommended view-section area of the video.

Another embodiment may have a method for streaming a video bitstreamfrom a server, configured to retrieve from the server information on asize and/or a position of one or more of a focus area within the videoonto which a decoding power for decoding the video should be focused,and a recommended view-section area of the video, and use theinformation in adaptively streaming the video bitstream from the server.

Still another embodiment may have a non-transitory digital storagemedium having stored thereon a computer program for performing a methodfor decoding a video bitstream having a video encoded thereinto, thedecoding being configured to derive from the video bitstream asignalization of a size and/or position of one or more of a focus areawithin the video onto which a decoding power for decoding the videoshould be focused, and a recommended view-section area of the video,when said computer program is run by a computer.

Another embodiment may have a non-transitory digital storage mediumhaving stored thereon a computer program for performing a method forstreaming a video bitstream from a server, configured to retrieve fromthe server information on a size and/or a position of one or more of afocus area within the video onto which a decoding power for decoding thevideo should be focused, and a recommended view-section area of thevideo, and use the information in adaptively streaming the videobitstream from the server, when said computer program is run by acomputer.

A first aspect of the present application is based on the finding thatstreaming media content pertaining to a temporally-varying spatial scenesuch as a video in a spatially unequal manner may be improved in termsof visible quality at comparable bandwidth consumption and/orcomputational complexity at a streaming reception site if the mediasegments selected and retrieved and/or a signalization obtained from theserver, provides the retrieving device with hints on a predeterminedrelationship to be complied with by qualities at which differentportions of the temporally-varying spatial scene are encoded into theselected and retrieved media segments. Otherwise, the retrieving devicemay not know beforehand as to which negative impact the juxtaposition ofportions encoded at different quality into the selected and retrievedmedia segment may have on the overall visible quality experienced by theuser. Information contained in the media segments and/or a signalizationobtained from the server such as, for instance, within a manifest file(media presentation description) or additional streaming related controlmessages from server to client such as SAND messages, enable theretrieving device to appropriately select among the media segmentsoffered at the server. In this manner, virtual reality streaming orpartial streaming of video content may be made more robust againstquality degradation as it could otherwise occur owing to an inadequatedistribution of the available bandwidth on to this spatial section ofthe temporally-varying spatial scene presented to the user.

A further aspect of the present invention is based on the finding thatstreaming of media content pertaining to a temporally-varying spatialscene such as a video in a spatially unequal manner such as using afirst quality at a first portion and a second, lower quality at a secondportion or with leaving a second portion being non-streamed, may beimproved in visible quality and/or may be made less complex in terms ofbandwidth consumption and/or computational complexity at the streamingretrieval side, by determining a size and/or position of the firstportion depending on information contained in the media segments and/ora signalization obtained from the server. Imagine, for instance, thetemporally-varying spatial scene would be offered at the server at atile-based manner for tile-based streaming, i.e. the media segmentswould represent spectral temporal portions of the temporally-varyingspatial scene each of which would be a temporal segment of the spatialscene within a corresponding tile of a distribution of tiles into whichthe spatial scene is sub-divided. In such a case, it is up to theretrieving device (client) to decide as to how to distribute theavailable bandwidth and/or computational power over the spatial scene,namely, at the granularity of tiles. The retrieving device would performthe selection of the media segments to the extent that a first portionof the spatial scene which follows respectively tracks atemporally-varying view section of the spatial scene, is encoded intothe selected and retrieved media segments in a predetermined qualitywhich may, for instance, be the highest quality feasible at the currentbandwidth and/or computational power conditions. A spatially neighboringsecond portion of the spatial scene may, for instance, not be encodedinto the selected and retrieved media segments, or may be encoded thereinto at a further quality, reduced relative to the predeterminedquality. In such a situation, it is a computationally complex matter, oreven not feasible, to compute a number/count of neighboring tiles, theaggregation of which completely covers the temporally-varying viewsection irrespective of the view section's orientation. Depending on theprojection chosen so as to map the spatial scene onto the individualtiles, the angular scene coverage per tile may vary over this scene andthe fact that the individual tiles may mutually overlap, even renders acomputation of a count of neighboring tiles sufficient to cover the viewsection in spatial terms, irrespective of the view section'sorientation, more difficult. Accordingly, in such a situation, theaforementioned information could indicate the size of the first portionas a count N of tiles or a number of tiles, respectively. By thismeasure, the device would be able to track the temporally-varying viewsection by selecting those media segments having the co-locatedaggregation of N tiles encoded there at the predetermined quality. Thefact that the aggregation of these N tiles sufficiently covers the viewsection may be guaranteed by way of the information indicating N.Another example would be information contained in the media segmentsand/or a signalization obtained from the server, which is indicative ofthe size of the first portion relative to a size of the view sectionitself. For example, this information could somehow set a “safety zone”or prefetch zone around the actual view section in order to account formovements of the temporally-varying view section. The larger the speedat which the temporally-varying view section moves across the spatialscene, the larger the safety zone should be. Accordingly, theaforementioned information could be indicative of the size of the firstportion in a manner relative to a size of the temporally-varying viewsection such as in an incremental or scaling manner. A retrieving devicesetting the size of the first portion according to such informationwould be able to avoid quality degradation which may otherwise occurowing to non-retrieved or low-quality portions of the spatial scenebeing visible in the view section. Here, it is irrelevant whether thisscene is offered in a tile-based manner or in some other manner.

Related to the just-mentioned aspect of the present application, a videobit stream having a video encoded there into, may be made decodable atan increased quality if the video bit stream is provided with asignalization of a size of a focus area within the video onto which adecoding power for decoding the video should be focused. By thismeasure, a decoder which decodes the video from the bit stream, couldfocus, or even restrict, its decoding power onto the decoding of thevideo onto a portion having the size of the focus area signalized in thevideo bit stream thereby knowing, for instance, that the thus-decodedportion is decodable by the available decoding power, and spatiallycovers a wanted section of the video. For instance, the size of thefocus area thus signalized could be selected to be large enough in orderto cover the size of the view section and a movement of this viewsection taking the decoding latency in decoding the video into account.Or, put differently, a signalization of a recommended view-section areaof the video contained in the video bitstream could allow the decoder totreat this area in an advantageous manner, thereby allowing the decoderto focus its decoding power accordingly. Irrespective of performingarea-specific decoding power focusing, the area signalization may beforwarded to a stage selecting on which media segments to download, i.e.where to place and how to dimension the portion of increased quality.

The first and second aspects of the present application are closelyrelated to a third aspect of the present application according to whichthe fact that a vast number of retrieving devices stream media contentfrom a server, is exploited, so as to gain information which maysubsequently be used in order to appropriately set the aforementionedtypes of information allowing to set the size, or size and/or position,of the first portion and/or appropriately set the predeterminedrelationship between the first and second quality. Thus, in accordancewith this aspect of the present application, the retrieving device(client) sends-out log messages logging one of a momentaneousmeasurement or a statistical value measuring a spatial position and/ormovement of the first portion, a momentaneous measurement or astatistical value measuring a quality of the temporally-varying spatialscene as far as is encoded into the selected media segments and as faras is visible in a view section, and a momentaneous measurement orstatistical value measuring the quality of the first portion or aquality of the temporally-varying spatial scene as far as is encodedinto the selected media segments and as far as is visible in a viewsection. Momentaneous measurements and/or statistical values may beprovided with time information concerning the time the respectivemomentaneous measurement or statistical value has been obtained. The logmessages may be sent to the server where the media segments are offered,or to some other device evaluating the inbound log messages so as toupdate, based thereon, current settings of the aforementionedinformation used to set the size, or size and/or position, of the firstportion and/or derive the predetermined relationship based thereon.

In accordance with a further aspect of the present application,streaming media content pertaining to a temporally-varying spatial scenesuch as a video, in particular in a tile-based manner, is made moreeffective in terms of avoidance of unavailing streaming trials byproviding a media presentation description which comprises at least oneversion at which the temporally-varying spatial scene is offered fortile-based streaming, with an indication of benefitting requirements forbenefitting from the tile-based streaming the respective version of thetemporally-varying spatial scene for each of the at least one version.By this measure, the retrieving device is able to match the benefittingrequirements of the at least one version with a device capability of theretrieving device itself or of another device interacting with theretrieving device with respect to tile-based streaming. For instance,the benefitting requirements could relate to decoding capabilityrequirements. That is, if the decoding power for decoding thestreamed/retrieved media content would not suffice to decode all mediasegments needed to cover a view section of the temporally-varyingspatial scene, then trying to stream and present the media content wouldbe a waste of time, bandwidth and computational power and accordingly,it would be more effective to not try it in any case. The decodingcapability requirements could, for instance, indicate a number ofdecoder instantiations necessitated for a respective version if, forinstance, the media segments relating to a certain tile form a mediastream such as a video stream, separate from media segments pertainingto another tile. The decoding capability requirement could, forinstance, also pertain to further information such as a certain fractionof decoder instantiations needed to fit to a predetermined decodingprofile and/or level, or could indicate a certain minimum capability ofa user input device to move in a sufficiently fast manner aviewport/section via which the user sees the scene. Depending on thescene content, a low movement capability may not suffice for the user tolook onto the interesting portions of the scene.

A further aspect of the present invention pertains to an extension ofstreaming of media content pertaining to temporally-varying spatialscenes. In particular, the idea in accordance with this aspect is that aspatial scene may in fact not only vary temporally but also in terms ofat least one further parameter suggest, for instance, views and aposition, view depth or some other physical parameter. The retrievingdevice may use adaptive streaming in this context by, depending on aviewport direction and the at least one further parameter, computingaddresses of media segments, the media segments describing a spatialscene varying in time and the at least one parameter, and retrieving themedia segments using the computed addresses from a server.

The above-outlined aspects of the present application and theiradvantageous implementations may be combined individually or alltogether.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present application are set forth below with respectto the Figures among which

FIG. 1 shows a schematic diagram illustrating a system of client andserver for virtual reality applications as an example as to where theembodiments set forth in the following figures may advantageously beused;

FIG. 2 shows a block diagram of a client device along with a schematicillustration of the media segment selection process in order to describea possible mode of operation of the client device in accordance with anembodiment of the present application where the server 10 provides thedevice with information on acceptable or endurable quality variationswithin the media content presented to the user;

FIG. 3 shows a modification of FIG. 2 , the portion of increase qualitydoes not concern the portion tracking the view section of viewport, buta region of interest of the media scene content as signaled from serverto client;

FIG. 4 shows a block diagram of the client device along with a schematicillustration of the media segment selection process in accordance withan embodiment where the server provides information on how to set asize, or size and/or position, of the portion of increased quality orthe size, or size and/or position, of the actually retrieved section ofthe media scene;

FIG. 5 shows a variant of FIG. 5 in that information sent by the serverdirectly indicates the size of portion 64, rather than scaling itdepending on expected movements of the viewport;

FIG. 6 shows a variant of FIG. 4 according to which the retrievedsection has the predetermined quality and its size is determined by theinformation stemming from the server;

FIGS. 7 a to 7 c show schematic diagrams illustrating the manner inwhich the information 74 according to FIGS. 4 and 6 increases the sizeof the portion retrieved at the predetermined quality via acorresponding enlargement of the size of the viewport;

FIG. 8 a shows a schematic diagram illustrating an embodiment whereclient device sends log messages to server or a certain evaluator forevaluating these log messages so as to derive thereof appropriatesettings, for instance, for the types of information discussed withrespect to FIGS. 2 to 7 c;

FIG. 8 b shows a schematic diagram of a tile-based cubic projection of a360 scene onto the tiles and an example of how some of the tiles arecovered by an exemplary position of a viewport. The small circlesindicate positions in the viewport equiangularly distributed, andhatched tiles are encoded at higher resolution in the downloadedsegments than tiles without hatching;

FIGS. 8 c and d show a schematic diagram of a diagram showing along atemporal axis (horizontal) as to how a buffer fullness (vertical axis)of different buffers of the client might develop, wherein FIG. 8 cassumes the buffers to be used to buffer representations coding specifictiles, while FIG. 8 d assumes the buffers to be used to bufferomnidirectional representations having the scene encoded thereinto atuneven quality, namely increased toward some direction specific for therespective buffer;

FIGS. 8 e and f show a three-dimensional diagram of different pixeldensity measurements within the viewport 28, differing in terms ofuniformity in spherical or viewplane sense;

FIG. 9 shows a block diagram of client device and a schematicillustration of the media segment selection process when the deviceinspects information stemming from the server in order to assess whethera certain version at which a tile-based streaming is offered by theserver, is acceptable for the client device or not;

FIG. 10 shows a schematic diagram illustrating the plurality of mediasegments offered by a server in accordance with an embodiment allowingfor a dependency of the media scene not only in time, but also inanother non-temporal parameter, namely here, exemplarily, scene centerposition; and

FIG. 11 shows a schematic diagram illustrating a video bit streamcomprising information steering or controlling a size of a focus areawithin the video encoded into the bit stream along with an example for avideo decoder able to take advantage of this information.

DETAILED DESCRIPTION OF THE INVENTION

In order to ease the understanding of the description of embodiments ofthe present application with respect to the various aspects of thepresent application, FIG. 1 shows an example for an environment wherethe subsequently described embodiments of the present application may beapplied and advantageously used. In particular, FIG. 1 shows a systemcomposed of client 10 and server 20 interacting via adaptive streaming.For instance, dynamic adaptive streaming over HTTP (DASH) may be usedfor the communication 22 between client 10 and server 20. However, thesubsequently outlined embodiments should not be interpreted as beingrestricted to the usage of DASH and likewise, terms such as mediapresentation description (MPD) should be understand as being broad so asto also cover manifest files defined differently than in DASH.

FIG. 1 illustrates a system configured to implement a virtual realityapplication. That is, the system is configured to present to a userwearing a head up display 24, namely via an internal display 26 of headup display 24, a view section 28 out of a temporally-varying spatialscene 30 which section 28 corresponds to an orientation of the head updisplay 24 exemplarily measured by an internal orientation sensor 32such as an inertial sensor of head up display 24. That is, the section28 presented to the user forms a section of the spatial scene 30 thespatial position of which corresponds to the orientation of head updisplay 24. In case of FIG. 1 , the temporally-varying spatial scene 30is depicted as an omni-directional video or spherical video, but thedescription of FIG. 1 and the subsequently explained embodiments arereadily transferrable to other examples as well, such as presenting asection out of a video with a spatial position of section 28 beingdetermined by an intersection of a facial access or eye access with avirtual or real projector wall or the like. Further, sensor 32 anddisplay 26 may, for instance, be comprised by different devices such asremote control and corresponding television, respectively, or they maybe part of a hand-held device such as a mobile device such as a tabletor a mobile phone. Finally, it should be noted that some of theembodiments described later on, may also be applied to scenarios wherethe area 28 presented to the user constantly covers the wholetemporally-varying spatial scene 30 with the unevenness in presentingthe temporally-varying spatial scene relating, for instance, to anunequal distribution of quality over the spatial scene.

Further details with respect to server 20, client 10 and the way thespatial content 30 is offered at server 20 is illustrated in FIG. 1 anddescribed in the following. These details should, however, also not betreated as limiting the subsequently explained embodiments, but shouldrather serve as an example of how to implement any of the subsequentlyexplained embodiments.

In particular, as shown in FIG. 1 , server 20 may comprise a storage 34and a controller 36 such as an appropriately programmed computer, anapplication-specific integrated circuit or the like. The storage 34 hasmedia segments stored thereon which represent the temporally-varyingspatial scene 30. A specific example will be outlined in more detailbelow with respect to the illustration of FIG. 1 . Controller 36 answersrequests sent by client 10 by re-sending to client 10 requested mediasegments, a media presentation description and may send to client 10further information on its own. Details in this regard are also set outbelow. Controller 36 may fetch requested media segments from storage 34.Within this storage, also other information may be stored such as themedia presentation description or parts thereof, in the other signalssent from server 20 to client 10.

As shown in FIG. 1 , server 20 may optionally in addition comprise astream modifier 38 modifying the media segments sent from server 20 toclient 10 responsive to the requests from the latter, so as to result atclient 10 in a media data stream forming one single media streamdecodable by one associated decoder although, for instance, the mediasegments retrieved by client 10 in this manner are actually aggregatedfrom several media streams. However, the existence of such a streammodifier 38 is optional.

Client 10 of FIG. 1 is exemplarily depicted as comprising a clientdevice or controller 40 or more decoders 42 and a reprojector 44. Clientdevice 40 may be an appropriately programmed computer, a microprocessor,a programmed hardware device such as an FPGA or an application specificintegrated circuit or the like. Client device 40 assumes responsibilityfor selecting segments to be retrieved from server 20 out of theplurality 46 of media segments offered at server 20. To this end, clientdevice 40 retrieves a manifest or media presentation description fromserver 20 first. From the same, client device 40 obtains a computationalrule for computing addresses of media segments out of plurality 46 whichcorrespond to certain, needed spatial portions of the spatial scene 30.The media segments thus selected are retrieved by client device 40 fromserver 20 by sending respective requests to server 20. These requestscontain computed addresses.

The media segments thus retrieved by client device 40 are forwarded bythe latter to the one or more decoders 42 for decoding. In the exampleof FIG. 1 , the media segments thus retrieved and decoded represent, foreach temporal time unit, merely a spatial section 48 out of thetemporally-varying spatial scene 30, but as already indicated above,this may be different in accordance with other aspects, where, forinstance, the view section 28 to be presented constantly covers thewhole scene. Reprojector 44 may optionally re-project and cut-out theview section 28 to be displayed to the user out of the retrieved anddecoded scene content of the selected, retrieved and decoded mediasegments. To this end, as shown in FIG. 1 , client device 40 may, forinstance, continuously track and update a spatial position of viewsection 28 responsive to the user orientation data from sensor 32 andinform reprojector 44, for instance, on this current spatial position ofscene section 28 as well as the reprojection mapping to be applied ontothe retrieved and decoded media content so as to be mapped onto the areaforming view section 28. Reprojector 44 may, accordingly, apply amapping and an interpolation onto a regular grid of pixels, forinstance, to be displayed on display 26.

FIG. 1 illustrates the case where a cubic mapping has been used to mapthe spatial scene 30 onto tiles 50. The tiles are, thus, depicted asrectangular sub-regions of a cube onto which scene 30 having the form ofa sphere has been projected. Reprojector 44 reverses this projection.However, other examples may be applied as well. For instance, instead ofa cubic projection, a projection onto a truncated pyramid or a pyramidwithout truncation may be used. Further, although the tiles of FIG. 1are depicted as being non-overlapping in terms of coverage of thespatial scene 30, the subdivision into tiles may involve a mutualtile-overlapping. And as will be outlined in more detail below, thesubdivision of scene 30 into tiles 50 spatially with each tile formingone representation as explained further below, is also not mandatory.

Thus, as depicted in FIG. 1 , the whole spatial scene 30 is spatiallysubdivided into tiles 50. In the example of FIG. 1 , each of the sixfaces of the cube is subdivided into 4 tiles. For illustration purposes,the tiles are enumerated. For each tile 50, server 20 offers a video 52as depicted in FIG. 1 . To be more precise, server 20 even offers morethan one video 52 per tile 50, these videos differing in quality Q #.Even further, the videos 52 are temporally subdivided into temporalsegments 54. The temporal segments 54 of all videos 52 of all tiles T #form, or are encoded into, respectively, one of the media segments ofthe plurality 46 of media segments stored in storage 34 of server 20.

It is again emphasized that even the example of a tile-based streamingillustrated in FIG. 1 merely forms an example from which many deviationsare possible. For instance, although FIG. 1 seems to suggest that themedia segments pertaining to a representation of the scene 30 at ahigher quality relate to tiles coinciding to tiles to which mediasegments belong which have the scene 30 encoded thereinto at quality Q1this coincidence is not necessary and the tiles of different qualitiesmay even correspond to tiles of a different projection of scene 30.Moreover, although not discussed so far, it may be that the mediasegments corresponding to different quality levels depicted in FIG. 1differ in spatial resolution and/or signal to noise ratio and/ortemporal resolution or the like.

Finally, differing from a tile-based streaming concept, according towhich the media segments which may be individually retrieved by device40 from server 20, relate to tiles 50 into which scene 30 is spatiallysubdivided, the media segments offered at server 20 may alternatively,for instance, each having the scene 30 encoded thereinto in a spatiallycomplete manner with a spatially varying sampling resolution, however,having sampling resolution maximum at different spatial positions inscene 30. For instance, that could be achieved by offering at the server20 sequences of segments 54 relating to a projecting of the scene 30onto truncated pyramids the truncated tip of which would be orientedinto mutually different directions, thereby leading to differentlyoriented resolution peaks.

Further, as to optionally present stream modifier 38, it is noted thatsame may alternatively be part of the client 10, or same may even bepositioned inbetween, within a network device via which client 10 andserver 20 exchange the signals described herein.

After having explained rather generally the system of server 20 andclient 10, the functionality of client device 40 with respect to anembodiment in accordance with a first aspect of the present applicationas described in more detail. To this end, reference is made to FIG. 2which shows device 40 in more detail. As already explained above, device40 is for streaming media content pertaining to the temporally-varyingspatial scene 30. As explained with respect to FIG. 1 , device 40 mayeither be configured so that the media content streamed pertainscontinuously to the whole scene in spatial terms, or merely a section 28thereof. In any case, device 40 comprises a selector 56 for selectingappropriate media segments 58 out of the plurality 46 of media segmentsavailable on server 20, and a retriever 60 for retrieving the selectedmedia segments from server 20 by respective requests such as HTTPrequests. As described above, selector 56 may use the media presentationdescription so as to compute the addresses of selected media segmentswith retriever 60 using these addresses in retrieving the selected mediasegments 58. For example, the computational rule to compute theaddresses indicated in the media presentation description may depend onquality parameter Q, tile T and some temporal segment t. The addressesmay be URLs, for instance.

As has also been discussed above, the selector 56 is configured toperform the selection so that the selected media segments have at leasta spatial section of the temporally-varying spatial scene and encodedthereinto. The spatial section may continuously cover the complete scenespatially. FIG. 2 illustrates at 61 the exemplary case where device 40adapts the spatial section 62 of scene 30 to overlap and surround viewsection 28. This is, however, as already noted above, not necessarilythe case and the spatial section may continuously cover the whole scene30.

Further, selector 56 performs the selection such that the selected mediasegments have section 62 encoded thereinto in a manner of spatiallyunequal quality. To be more precise, a first portion 64, indicated byhatching in FIG. 2 , of spatial section 62 is encoded into the selectedmedia segment at a predetermined quality. This quality may, forinstance, be the highest quality offered by server 20, or may be a“good” quality. Device 42 moves, for instance, or adapts the firstportion 64 in a manner so as to spatially follow the temporally-varyingview section 28. For instance, selector 56 selects the current temporalsegments 54 of those tiles inheriting the current position of viewsection 28. In doing so, selector 56 may, optionally, as explained withrespect to further embodiments hereinafter, keep the number of tilesmaking-up first portion 64 constant. In any case, a second portion 66 ofsection 62 is encoded into the selected media segments 58 at anotherquality such as a lower quality. For example, selector 56 selects themedia segments corresponding to the current temporal segments of tilesspatially neighboring the tiles of portion 64 and belonging to the lowerquality. For instance, selector 56 mainly selects the media segmentscorresponding to portion 66 for the sake of addressing the possibleoccasion where view section 28 moves too fast so as to leave portion 64and overlap portion 66 before the temporal interval corresponding to thecurrent temporal segment ends and selector 56 would be able to newlyspatially arrange portion 64. In this situation, the portion of section28 protruding into portion 66 may be presented to the user nevertheless,namely at reduced quality.

It is, not possible for device 40 to assess as to which negative qualitydegradation may result from preliminarily presenting to the user reducedquality scene content along with the scene content within portion 64which is of the higher quality, to the user. In particular, a transitionbetween these two qualities results which may be clearly visible to theuser. At least, such transitions may be visible depending on the currentscene content within section 28. The severity of the negative impact ofsuch a transition within the view of the user is a characteristic of thescene content as offered by server 20 and may not be forecast by device40.

Accordingly, in accordance with the embodiment of FIG. 2 , device 40comprises a deriver 66 deriving a predetermined relationship to befulfilled between the quality of portion 64 and the quality of portion66. Deriver 66 derives this predetermined relationship from informationwhich may be contained in the media segments such as within transportboxes within the media segments 58 and/or contained in a signalizationobtained from server 20 such as within the media presentationdescription or proprietary signals sent from server 20 such as SANDmessages or the like. Examples as to how the information 68 would looklike, are presented in the following. The predetermined relationship 70derived by deriver 66 on the basis of information 68 is used by selector56 in order to appropriately perform the selection.

For instance, the restriction in selecting the qualities of portions 64and 66 compared to a completely independent selection of qualities forportion 64 and 66 influences a distribution of available bandwidth forretrieving the media contents concerning section 62 onto portions 64 and66. In any case, selector 56 selects the media segments such that thequalities at which portions 64 and 66 are encoded into the mediasegments finally retrieved fulfill the predetermined relationship.Examples as to how the predetermined relationship might look are alsoset out below.

The media segments selected and finally retrieved by retriever 60 arefinally forwarded to the one or more decoders 42 for decoding.

In accordance with a first example, for instance, the signalingmechanism embodied by information 68 involves information 68 indicatingto device 40, which may be a DASH client, which quality combinations areacceptable for the offered video content. For example, the information68 could be a list of quality pairs that indicate to the user or device40 that the different regions 64 and 66 can be mixed with a maximumquality (or resolution) difference. Device 40 may be configured toinevitably use a certain quality level such as the highest one offeredat sever 10, for portion 64 and derive quality levels at which portion66 may be coded into the selected media segments from information 68wherein same be contained in form of a list of quality levels forportion 68, for instance.

The information 68 could indicate an endurable value for a measure of adifference between the quality of portion 68 and the quality of portion64. As a “measure” of the difference in quality, a quality index of themedia segments 58, by way of which the same are distinguished in themedia presentation description and by way of which the addresses of thesame are computed using the computational rule described in the mediapresentation description, may be used. In MPEG-DASH, the correspondingattribute indicating the quality would be, for instance, at@qualityRanking. Device 40 could take the restriction in selectablequality level pairs at which portions 64 and 66 may be coded into theselected media segments into account in performing the selection.

However, instead of this difference measure, the difference in qualitycould alternatively be measured, for instance, in bit rate difference,i.e., an endurable difference in bit rate at which portions 64 and 66are encoded into the corresponding media segments, respectively,assuming that the bit rate usually monotonically increases withincreasing quality. The information 68 could indicate allowed pairs ofoptions for qualities at which portions 64 and 66 are encoded into theselected media segments. Alternatively, the information 68 simplyindicates allowed qualities for coding portion 66, thereby indirectlyindicating allowed or endurable quality differences assuming that mainportion 64 is encoded using some default quality such as, for instance,the highest quality possible or available. For instance, information 68could be a list of acceptable representation IDs or could indicate aminimum bit rate level with respect to the media segments concerningportion 66.

However, a more gradual quality difference could alternatively bedesired, wherein, instead of quality pairs, quality groups (more thantwo qualities) could be indicated, wherein, dependent on the distance tosection 28, i.e., the viewport, the quality difference could beincreased. That is, the information 68 could indicate the endurablevalue for the measure of a difference between the qualities for portion64 and 66 in a manner depending on a distance to view section 28. Thiscould be done by way of a list of pairs of a respective distance to theview section and a corresponding endurable value for the measure of thedifference in quality beyond the respective distance. Below therespective distance, the quality difference has to be lower. That is,each pair would indicate for a corresponding distance that a part withinportion 66, further away from section 28 than the correspondingdistance, may have a quality difference to the quality of portion 64exceeding the corresponding endurable value of this list entry.

The endurable value may increase within increasing distance to viewsection 28. The acceptance of the just discussed quality difference isoften dependent on the time that these different qualities are shown tothe user. For instance, content with a high quality difference might beacceptable if it is only shown for 200 microseconds, while content witha lower quality difference might be acceptable if it is shown for 500microseconds. Therefore, in accordance with a further example, theinformation 68 could also include, in addition to the aforementionedquality combinations, for instance, or in addition to the allowedquality difference, a time interval for which the combination/qualitydifference may be acceptable. In other words, the information 68 mayindicate an endurable or maximally allowed difference between thequalities of portions 66 and 64 along with an indication of a maximallyallowed time interval for which portion 66 may be shown within the viewsection 28 concurrently with portion 64.

As already noted previously, the acceptance of quality differencesdepends on the content itself. For instance, the spatial position of thedifferent tiles 50 has an influence on the acceptance. Qualitydifferences in a uniform background region with low frequency signalsare expected to be more acceptable than quality differences in aforeground object. Furthermore, the position in time also has aninfluence on the acceptance rate due to changing content. Therefore,according to another example, signals forming information 68 are sent todevice 40 intermittently such as, for instance, per representation orperiod in DASH. That is, the predetermined relationship indicated byinformation 68 may be intermittently updated. Additionally and/oralternatively, the signaling mechanism realized by information 68 mayvary in space. That is, the information 68 may be made spatiallydependent such as, by way of an SRD parameter in DASH. That is,different predetermined relationships may be indicated by information 68for different spatial regions of scene 30.

The embodiment of device 40, as described with respect to FIG. 2 ,pertains to the fact that device 40 wants to keep quality degradations,due to pre-fetched portions 66, within the retrieved section 62 of videocontent 30 briefly being visible in section 28 before being able tochange the position of section 62 and portion 64 so as to adapt the sameto the change in position by section 28, as low as possible. That is, inFIG. 2 , portions 64 and 66, the qualities of which were restricted asfar as their possible combinations were concerned by way of information68, were different portions of section 62 with a transition between bothportions 64 and 66 being continuously shifted or adapted in order totrack or run-ahead the moving view section 28. In accordance with analternative embodiment shown in FIG. 3 , device 40 uses information 68in order to control possible combinations of qualities of portions 64and 66 which, however, in accordance with the embodiment of FIG. 3 , aredefined to be portions differentiated or distinguished from one anotherin a manner defined, for instance, in the media presentationdescription, i.e., defined in a manner independent from a position ofview section 28. The positions of portions 64 and 66 and the transitionthere between may be constant or vary in time. If varying in time, thevariation is due to a change in content of scene 30. For example,portion 64 would correspond to a region of interest for which theexpenditure of higher quality is worthwhile, while portion 66 is aportion for which quality reduction owing to low bandwidth conditions,for instance, should be considered prior to considering qualityreductions for portion 64.

In the following, a further embodiment for an advantageousimplementation of device 40 is described. In particular, FIG. 4 showsdevice 40 in a manner corresponding, in structure, to FIGS. 2 and 3 butthe mode of operation is changed so as to correspond to a second aspectof the present application.

That is, device 40 comprises a selector 56, a retriever 60 and a deriver66. The selector 56 selects from the media segments 58 of the plurality46 offered by server 20 and retriever 60 retrieves the selected mediasegments from the server. FIG. 4 presumes that device 40 operates asdepicted and illustrated with respect to FIGS. 2 and 3 , namely thatselector 56 performs the selection so that the selected media segments58 have a spatial section 62 of scene 30 encoded thereinto in a mannerwhere this spatial section follows view section 28 which varies itsspatial position in time. However, a variant corresponding to the sameaspect of the present application is described later on with respect toFIG. 5 , wherein, for each time instant t, the selected and retrievedmedia segments 58 have the whole scene or a constant spatial section 62encoded thereinto.

In any case, selector 56 selects, similar to the description withrespect to FIGS. 2 and 3 , the media segments 58 such that a firstportion 64 within section 62 is encoded into the selected and retrievedmedia segments at a predetermined quality, whereas a second portion 66of section 62, which spatially neighbors the first portion 64, isencoded into the selected media segments at a reduced quality relativeto the predetermined quality of portion 64. A variant where selector 56restricts the selection and retrieval to media segments pertaining to amoving template tracking the position of viewport 28 and wherein themedia segments have encoded thereinto the section 62 completely at thepredetermined quality so that the first portion 64 completely coverssection 62 while being surrounded by non-encoded portion 72 is depictedin FIG. 6 . In any case, selector 56 performs the selection so that thefirst portion 64 follows the view section 28 which varies in spatialposition temporally.

In such a situation, it is also not easy to forecast by client 40 as tohow large section 62 or portion 64 should be. Depending on the scenecontent, most users may act similarly in moving view section 28 acrossscene 30 and, accordingly, the same applies to the interval of viewsection 28 speeds at which view section 28 may presumably move acrossscene 30. Accordingly, in accordance with the embodiment of FIGS. 4 to 6, information 74 is provided by server 20 to device 40 so as to assistdevice 40 in setting a size, or size and/or position, of the firstportion 64, or the size, or size and/or position, of section 62,respectively, dependent on the information 74. With respect to thepossibilities of transmitting information 74 from server 20 to device40, the same applies as described above with respect to FIGS. 2 and 3 .That is, the information may be contained within the media segments 58such as within event boxes thereof, or a transmission within the mediapresentation description or proprietary messages sent from server todevice 40, such as SAND messages, may be used to this end.

That is, in accordance with the embodiments of FIGS. 4 to 6 , selector56 is configured to set a size of the first portion 64 depending oninformation 74 stemming from server 20. In the embodiments illustratedin FIGS. 4 to 6 , the size is set in units of tiles 50, but, as alreadydescribed above with respect to FIG. 1 , the situation may be slightlydifferent when using another concept of offering scene 30 in spatiallyvarying quality at server 20.

In accordance with an example, information 70 could, for instance,include a probability for a given movement speed of viewport of viewsection 28. Information 74 could, as already denoted above, resultwithin the media presentation description made available for clientdevice 40 which may, for instance, be a DASH client, or some in-bandmechanisms may be used to convey information 74 such as event boxes,i.e., EMSG or SAND messages in case of DASH. The information 74 couldalso be included in any container format such as ISO file format ortransport format beyond MPEG-DASH such as MPEG-2TS. It could also beconveyed in the video bitstream such as in SEI messages as describedlater. In other words, the information 74 may indicate a predeterminedvalue for a measure of a spatial speed of view section 28. In thismanner, the information 74 is indicative of the size of portion 64 inthe form of a scaling, or in the form of an increment relative to a sizeof view section 28. That is, information 74 starts from some “base size”for portion 64 used to cover the size of section 28 and increases this“base size” appropriately such as incrementally or by scaling. Forexample, the aforementioned movement speed of view section 28 could beused to correspondingly scale the circumference of a current position ofview section 28 so as to determine, for instance, the furthest positionsof the circumference of view section 28 along any spatial directionfeasible after this time interval, for example, determining the latencyin adjusting the spatial location of portion 64 such as, for instance,the time duration of the temporal segments 54 corresponding to thetemporal length of media segments 58. The speed times this time durationadds to the circumference of a current position of viewport 28,omni-directional, could thus result into such a worst case circumferenceand could be used to determine an enlargement of portion 64 relative tosome minimum expansion of portion 64 assuming a non-moving viewport 28.

Information 74 may even be related to an evaluation of statistics ofuser behavior. Later on, embodiments are described which are suitablefor feeding such an evaluation process. For instance, information 74could indicate maximum speeds with respect to certain percentages ofusers. For example, information 74 could indicate that 90% of users moveat a speed lower than 0.2 rad/s and 98% of users move at a speed lowerthan 0.5 rad/s. The information 74 or the messages carrying the samecould be defined in such a way that probability-speed pairs are definedor a message could be defined that signals the maximum speed for a fixedpercentage of users, e.g., for 99% of the users. The movement speedsignaling 74 could additionally comprise directional information, i.e.,an angle in 2D or 2D plus depth in 3D also known as light fieldapplication. Information 74 would indicate different probability-speedpairs for different movement directions.

In other words, information 74 may apply to a given time span such as,for instance, the temporal length of a media segment. It may consist oftrajectory-based (x percentile, average user path) or velocity-basedpairs (x percentile, speed) or distance-based pairs (x percentile,aperture/diameter/advantageous) or area-based pairs (x percentile,recommended area) or single maximal boundary values for path, velocity,distance or advantageous area. Instead of relating the information topercentiles, a simple frequency ranking could be done according to mostof the users move at a certain speed, second most users move at afurther speed and so on. Additionally or alternatively, information 74is not restricted to indicate the speed of view section 28, but couldlikewise indicate an advantageous area to be viewed respectively todirect the portion 62 and/or 64 which is sought to track view section 28to, with or without an indication about statistical significance of theindication such as percentage of users having complied with thatindication or indication of whether the indication coincides with theuser viewing speeds/view sections having been logged most often, andwith or without temporal persistence of the indication. Information 74could indicate another measure of the speed of view section 28, such asa measure for a travelling distance of view section 28 within a certainperiod in time, such as within a temporal length of the media segmentsor, in more detail, the temporal length of temporal segments 54.Alternatively, information 74 could be signaled in a mannerdistinguishing between certain directions of movement into which viewsection 28 may travel. This pertains to both an indication of speed orvelocity of view section 28 into a certain direction as well as theindication of traveled distance of view section 28 with respect to acertain direction of movement. Further, the expansion of portion 64could be signaled by way of information 74 directly, eitheromni-directionally or in a manner discriminating different movementdirections. Furthermore, all of the just outlined examples may bemodified, in that the information 74 indicates these values along with apercentage of users for which these values suffice in order to accountfor their statistical behavior in moving view section 28. In thisregard, it should be noted that the view speed, i.e., the speed of viewsection 28 may be considerable and is not restricted to speed values fora user head, for instance. Rather, the view section 28 could be moveddepending on the user's eye movement, for instance, in which case theview speed may be considerably larger. The view section 28 could also bemoved according to another input device movement such as according tothe movement of a tablet or the like. As all these “input possibilities”enabling the user to move section 28 result in different expected speedsof view section 28, information 74 may even be designed such that itdistinguishes between different concepts for controlling the movement ofview section 28. That is, information 74 could indicate or be indicativeof the size of portion 64 in a manner indicating different sizes fordifferent ways of controlling the movement of view section 28 and device40 would use the size indicated by information 74 for the correct viewsection control. That is, device 40 gains knowledge about the way viewsection 28 is controlled by the user, i.e., checks whether view section28 is controlled by head movement, eye movement or tablet movement orthe like and sets the size in accordance with that part of information74 which corresponds to this kind of view section control.

Generally, the movement speed can be signaled per content, period,representation, segment, per SRD position, per pixel, per tile, e.g., onany temporal or spatial granularity or the like. The movement speed canalso be differentiated in head movement and/or eye movement, as justoutlined. Further, the information 74 about user movement probabilitymay be conveyed as a recommendation about high resolution prefetch,i.e., video area outside user viewport, or spherical coverage.

FIG. 7 a to FIG. 7 c briefly summarize some of the options explainedwith respect to information 74 in the way it is used by device 40 toamend the size of portion 64 or portion 62, respectively, and/or theposition thereof. In accordance with the option shown in FIG. 7 a ,device 40 enlarges the circumference of section 28 by a distancecorresponding to a product of the signaled speed v and the time durationΔt, which may correspond to the time period which corresponds to thetemporal length of the temporal segments 54 encoded in the individualmedia segments 50 a. Additionally and/or alternatively, the position ofportion 62 and/or 64 may be placed the farther away from a currentposition of section 28, or the current position of portion 62 and/or 64into direction of the signaled speed or movement as signaled byinformation 74, the larger the speed is. The speed and direction may bederived from surveying or extrapolating a recent development or changein recommended area indication by information 74. Instead ofomni-directionally applying v×Δt, the speed may be signaled byinformation 74 different for different spatial directions. Thealternative depicted in FIG. 7 d shows that information 74 may indicatethe distance of enlarging the circumference of view section 28 directly,with this distance being indicated by parameter s in FIG. 7 b . Again, adirectionally varying enlargement of section may be applied. FIG. 7 cshows that the enlargement of the circumference of section 28 could beindicated by information 74 by area increase such as, for instance, inthe form of the ratio of the area of the enlarged section compared tothe original area of section 28. In any case, the circumference of area28, after enlargement, indicated by 76 in FIGS. 7 a to 7 c could be usedby selector 56 to dimension or set the size of portion 64 such thatportion 64 covers the whole area within enlarged section 76 on at leasta predetermined amount thereof. Obviously, the larger section 76, thelarger the number of tiles, for instance, is within portion 64. Inaccordance with a further alternative, section 74 could indicate thesize of portion 64 directly such as in the form of number of tilesmaking up portion 64.

The latter possibility of signaling the size of portion 64 is depictedin FIG. 5 . The embodiment of FIG. 5 could be modified in the samemanner as the embodiment of FIG. 4 was modified by the embodiment ofFIG. 6 , i.e., the complete area of section 62 could be fetched fromserver 20 by way of segments 58 at the quality of portion 64.

In any case, at the very end of FIG. 5 , information 74 distinguishesbetween different sizes of view section 28, i.e., between differentfield of views seen by view section 28. Information 74 simply indicatesthe size of portion 64 depending on the size of view section 28 whichdevice 40 currently aims at. This enables the service of server 20 to beused by devices with different field of views or different sizes of viewsection 28 without devices such as device 40 having to cope with theproblem of computing or otherwise guessing the size of portion 64 sothat portion 64 suffices to cover view section 28 irrespective of anymovement of section 28 as discussed with respect to FIGS. 4, 6 and 7 .As may have become clear from the description of FIG. 1 , it is all buteasy to assess as to which constant number of tiles, for instance, maysuffice to completely cover a certain size of view section 28, i.e., acertain field of view, irrespective of the view section 28's directionfor spatial positioning 30. Here, information 74 alleviates thissituation and device 40 is able to simply look-up within information 74the value of the size of portion 64 to be used for the size of viewsection 28 applying to device 40. That is, in accordance with theembodiment of FIG. 5 , the media presentation description made availablefor the DASH client or some in-bent mechanisms, such as event boxes orSAND messages, could include information 74 about the spherical coverageor field of view of sets of representations or sets of tiles,respectively. One example could be a tiled offering with Mrepresentations as depicted in FIG. 1 . The information 74 couldindicate the recommended number n<M of tiles (called representations) todownload for coverage of a given end device field of view, e.g., out ofa cubic representation tiled into 6×4 tiles as depicted in FIG. 1 , 12tiles are deemed sufficient to cover a 90°×90° field of view. Due to theend device field of view not always being perfect aligned with the tileboundaries, this recommendation cannot be trivially generated by device40 on its own. Device 40 may use information 74 by downloading, forinstance, at least N tiles, i.e., the media segments 58 concerning Ntiles. Another way to utilize the information would be to emphasize thequality of N tiles within section 62 that are closest to the currentview center of the end device, i.e., use N tiles for making up portion64 of section 62.

With respect to FIG. 8 a , an embodiment with respect to a furtheraspect of the present application is described. Here, FIG. 8 a showsclient device 10 and server 20 which communicate with each other inaccordance with any of the possibilities described above with respect toFIGS. 1 to 7 . That is, device 10 may be embodied in accordance with anyof the embodiments descried with respect to FIGS. 2 to 7 or may simplyact without these specifics in the manner described above with respectto FIG. 1 . However, favorably, device 10 is embodied in accordance withany of the embodiments described above with respect to FIGS. 2 to 7 orany combination thereof and additionally inherits the mode of operationdescribed now with respect to FIG. 8 a . In particular, device 10 isinternally construed as has been described above with respect to FIGS. 2to 8 , i.e., device 40 comprises selector 56, retriever 60 and,optionally, deriver 66. Selector 56 performs the selection for aiming atunequal streaming, i.e., selecting the media segments in a manner sothat the media content is encoded into the selected and retrieved mediasegments in a manner so that the quality spatially varies and/or in amanner so that there are non-encoded portions. However, in addition tothis, device 40 comprises a log message sender 80 which sends-out toserver 20 or an evaluation device 82 log messages logged in, forinstance,

-   -   a momentaneous measurement or a statistical value measuring a        spatial position and/or movement of the first portion 64,    -   a momentaneous measurement or a statistical value measuring a        quality of the temporally-varying spatial scene as far as        encoded into selected media segments and as far as visible in        view section 28, and/or    -   a momentaneous measurement or a statistical value measuring the        quality of the first portion or a quality of the        temporally-varying spatial scene 30 as far as encoded into the        selected media segments and as far as visible in view section        28.

The motivation is as follows.

In order to be able to derive statistics, such as the most interestingregions or speed-probability pairs, as described previously, reportingmechanisms from users are used. Additional DASH Metrics to the onesdefined in Annex D of ISO/IEC23009-1 are used.

One metric would be the FoV of Client as DASH Metric, where DASH clientssend back to a Metric Server (it could be the same as the DASH server oranother one) the characteristics of the end device in term of FoV.

Key Type Description EndDeviceFoVH Integer Horizontal FoV of end devicein degree EndDeviceFoVV Integer Vertical FoV of end device in degree

One Metric would be ViewportList, where DASH clients send back to aMetric Server (it could be the same as the DASH server or another one)the viewport watched by each client in time. An instantiation of such amessage could be as follows:

Key Type Description ViewportList List List of Viewport over time EntryObject An entry for a single Viewport time Integer Playout-time(media-time) at which the following viewport is chosen by the client.roll Integer The roll component of the orientation of the Viewport pitchInteger The pitch coordinate of the orientation of the Viewport yawInteger The yaw coordinate of the orientation of the Viewport

For the Viewport (region of interest) message, the DASH client could beasked to report whenever a Viewport change occurs, with potentially agiven granularity (with or without avoiding reporting of very smallmovements) or with a given periodicity. Such a message could be includedin the MPD as an attribute @reportViewPortPeriodicity or an element ordescriptor. It could be also indicated out of band, such as with a SANDmessage or any other means.

Viewport can also be signalled on tile granularity.

Additionally or alternatively, log messages could report on othercurrent scene related parameters changing responsive to user input, suchas any of the parameters discussed below with respect to FIG. 10 such ascurrent user distance from the scene centre and/or the current viewdepth.

Another metric would be the ViewportSpeedList, where DASH clientsindicate the movement speed for a given viewport in time when a movementhappens.

Key Type Description ViewportSpeedList List List of Viewport changespeed over time Entry Object An entry for a single Viewport change speedtime Integer Playout-time (media-time) at which the following viewportis chosen by the client. roll Integer The roll component of theorientation of the Viewport pitch Integer The pitch coordinate of theorientation of the Viewport yaw Integer The yaw coordinate of theorientation of the Viewport speed_roll Integer The speed in rollcomponent of the orientation of the Viewport speed_pitch Integer Thespeed in pitch component of the orientation of the Viewport speed_yawInteger The speed in yaw component of the orientation of the Viewport

This message would be sent only if the client performs a viewportmovement. However, the server could, as well as for the previous case,indicate that the message should be only sent if the movement issignificant. Such a configuration could be something like@minViewportDifferenceForReporting signalling the size in pixels orangle or any other magnitude that needs to have changed for a message tobe sent.

Another important thing for a VR-DASH service, where asymmetric qualityis offered as described above, is to evaluate how fast users switch froman asymmetric representation or a set of unequal quality/resolutionrepresentations for a Viewport to another representation or set ofrepresentation more adequate for another viewport. With such a metric,Servers could derive statistics that help them to understand relevantfactors that impact the QoE. Such a metric could look like:

Key Type Description LowQualityDurationAtSwitchList List List of timeintervals used to switch from the low quality content to the highquality content in the VR-DASH service. How long the low quality contenthas been played for a new Viewport before the high quality content forthe new Viewport is available. Entry Object An entry for a singleinterval duration of the switch to high-quality content for anotherViewport time Integer Playout-time (media-time) at which the followingviewport is chosen by the client. duration Integer The duration of theplayback of the low quality version of the new Viewport when a Viewportchange occurs

Alternatively, the duration described before could be given as anaverage:

Key Type Description LowQualityAvgDurationAtSwitchList List Average oftime intervals used to switch from the low quality content to the highquality content in the VR-DASH service. How long the long qualitycontent has been played for a new Viewport before the high qualitycontent for the new Viewport is available. avgDuration Integer Theaverage duration of the playback of the low quality version of the newViewport when a Viewport change occurs

All of these metrics could additionally have the time at which themeasurement has been performed, as for other DASH Metrics.

t Real-Time Time of the measurement of the parameter.

In some cases, it could happen that if unequal quality content isdownloaded and bad quality (or a mixture of good and bad quality) isshown for a long enough time (which could be only a couple of seconds)the user is unhappy and leaves the session. Conditional to leaving thesession the user could send a message of the quality shown in the last xtime-interval:

Key Type Description ShownQualityList List List of Quality shown in thelast time. Entry Object An entry for a single interval duration of theshown quality duration Integer Duration of the reported quality. qualitycomma- The quality rank values of the separated viewport quality rankvalues

Alternatively, a max-quality difference could be reported or themax_quality and min_quality of the viewport

As became clear from the above description relating to FIG. 8 a , inorder for a tile-based DASH streaming service operator to set up andoptimize its service in a meaningful fashion (e.g. with respect toresolution ratios, bitrates and segment durations) it is advantageous ifthe service operator is able to derive statistics which uses clientreporting mechanisms examples of which were described above. AdditionalDASH Metrics to the ones defined above and in addition to Annex D of[A1] are set out hereinafter.

Imagine a tile-based streaming service using video with a cubicprojection as depicted in FIG. 1 . The reconstruction on client side isillustrated in FIG. 8 b , in which small circles 198 indicateprojections of a two-dimensional distribution of view directions, withinthe viewport 28 of the client, equiangularly distributed horizontallyand vertically, onto the picture areas covered by the individual tiles50. Tiles marked hatched indicate high-resolution tiles, thus forming ahigh-resolution portion 64, while tile 50 shown non-hatched representlow-resolution tiles, thus forming the low-resolution portion 66. It canbe seen that the user is presented partially low-resolution tiles as theviewport 28 changed since the last update to the segment selection anddownload which determines the resolution of each tile on the cube onwhich the projection planes or pixel arrays of the tiles 50 coded intothe downloadable segments 58 lie.

While the above description rather generally, inter alias, indicated afeedback or log message which indicates the quality at which the videois presented to the user in the viewport, in the following, a morespecific and advantageous metric applicable in this regard shall beoutlined. The metric described now could be reported back from clientside and be referred to as Effective Viewport Resolution. It is supposedto indicate to the service operator the effective resolution in theviewport of the client. In case the reported effective viewportresolutions indicates that a user was only presented a resolutiontowards the resolution of the low-resolution tiles, a service operatorcould change the tiling configuration, resolution ratios or segmentlength accordingly to achieve a higher effective viewport resolution.

One embodiment would be the average pixel count in the viewport 28,measured in the projection plan where the pixel array of the tiles 50 ascoded into the segments 58 lies. The measurement could distinguishbetween, or be specific for, horizontal direction 204 and verticaldirection 206 in relation to the covered Field of View (FoV) of theviewport 28. The following table shows a possible example for suitablesyntax and semantics which could be contained in log messages so as tosignal the outlined viewport quality measure.

Key Type Description EffectiveRes Object EffectiveViewportResolutionEffectiveViewportResolutionH Integer Average horizontal effectiveresolution within viewport during reporting periodEffectiveViewportResolutionV Integer Average vertical effectiveresolution within viewport during reporting period

The breakdown into horizontal and vertical direction could be left offwith using a scalar value for the average pixel count instead. Alongwith an indication of the aperture or size of the viewport 28 whichmight also be reported to the recipient of the log messages, namelyevaluator 82, the average count is indicative of the pixel densitywithin the viewport.

It may be advantageous to reduce the FoV considered for the metric to besmaller than the FoV of the viewport actually presented to the user,thereby excluding areas towards the boundaries of the viewport that areonly used for peripheral vision and hence do not have an impact onsubjective quality perception. This alternative is illustrated by adashed line 202 which encircles pixels lying in such a central sectionof the viewport 28. The reporting of the considered FoV 202 for thereported metric in relation to the viewport's 28 overall FoV, might alsobe signalled to the log message recipient 82. The following table showsa corresponding extension of the previous example.

Key Type Description EffectiveRes Object EffectiveViewportResolutionConsideredFoV_H Integer Horizontal portion around the center of theviewport used for gathering the pixel count ConsideredFoV_V IntegerVertical portion around the center of the viewport used for gatheringthe pixel count EffectiveFoVResolutionH Integer Average horizontaleffective resolution within ConsideredFoV_H of viewport of duringreporting period EffectiveFoVResolutionV Integer Average verticaleffective resolution within ConsideredFoV_V of viewport during reportingperiod

According to a further embodiment, the average pixel density is notmeasured by averaging the quality in a spatially uniform manner in theprojection plane as effectively the case in the example described so farwith respect to the examples containing EffectiveFoVResolutionH/V, butin a manner weighting this averaging in a non-uniform manner over thepixels, i.e. the projection plane. The averaging may be performed in aspherically uniform manner. As an example, averaging may be performeduniform with respect to sample points distributed as the circles 198are. In other words, the averaging may performed by weighting the localdensities by a weight decreasing in a quadratic manner with increasinglocal projection plane distance and increasing according to sine oflocal tilt of the projection against the line connecting with the viewpoint. The message may include an optional (flag controlled) step toadjust for the inherent oversampling of some of the availableprojections (such as Equirectangular Projection), e.g. by using anuniform sphere sampling grid. Some projections do not have a bigoversampling issue and forcing computing removal of oversampling mightlead to unnecessary complexity issues. This must not be limited toEquirectangular Projection. Reporting does not need to distinguishhorizontal and vertical resolution but can combine them. The followinggives one embodiment.

Key Type Description EffectiveRes Object EffectiveViewportResolutionSphereOversamplingCompensationFlag Integer When equal to 0, pixel countfor effectiveResolution is derived on the projected frame sampling grid.When equal to 1, pixel count for effectiveResolution is derived on the auniform spherical sampling grid. ConsideredFoV_H Integer Horizontalportion around the center of the viewport used for gathering the pixelcount ConsideredFoV_V Integer Vertical portion around the center of theviewport used for gathering the pixel count EffectiveFoVResolutionHInteger Average horizontal effective resolution within ConsideredFoV_Hof viewport of during reporting period EffectiveFoVResolutionV IntegerAverage vertical effective resolution within ConsideredFoV_V of viewportduring reporting period

Applying an equiangular uniformity in averaging, is illustrated in FIG.8 e by showing how equiangularly horizontally and vertically distributedpoints 302 on a sphere 304 centered at the viewpoint 306 are, as far asbeing within the viewport 28, projected onto the projection plane 308 ofthe tile, here a cube, so as to perform the averaging of the pixeldensity of the pixels 308 arranged in an array, in columns and rows, inthe projection area, so as to set the local weight for the pixel densityaccording to the local density of the projections 198 of the points 302onto the projection plane. A quite similar approach is depicted in FIG.8 f . Here, points 302 are equi-distantly distributed, i.e. uniformlyhorizontally and vertically in columns and rows, in a viewport planeperpendicular to the view direction 312, and the projection ontoprojection plane 308 defines the points 198, the local density of whichcontrols the weight at which the local density pixel density 308(varying because of high and low resolution tiles within viewport 28,contribute to the average. The alternative of FIG. 8 f may be usedinstead of the one depicted in FIG. 8 e in the above examples such asthe most recent table.

In the following, an embodiment for a further sort of log message isdescribed which is related to DASH clients 10 having multiple mediabuffers 300 as exemplarily depicted in FIG. 8 a , i.e. DASH clients 10forwarding the downloaded segments 58 to the subsequent decoding by theone or more decoder 42 (cp. FIG. 1 ). The distribution of the segments58 onto the buffers could be made in different manners. For example thedistribution could be made so that certain regions of a 360 video aredownloaded separately from each other, or buffered after download intoseparate buffers. The following examples illustrate differentdistributions by indicating as to which tiles T indexed #1 to #24 asshown in FIG. 1 (antipodes have a sum of 25) are encoded into whichindividually downloadable representation R #1 to #P at which Quality Qof Qualities #1 to #M (with 1 being the best and M being the worst), andhow these P representations R could be grouped into adaptation sets Aindexed #1 to #S in the MPD (optional) and how the segments 58 of the Prepresentations R could be distributed onto the buffer of buffers Bindexed #1 to #N:

R T Q T Q T Q T Q T Q T Q A buffer 1 1 1 5 — 9 — 13 — 17 — 21 — 1 1 2 —6 — 10 — 14 — 18 — 22 — 3 — 7 — 11 — 15 — 19 — 23 — 4 — 8 — 12 — 16 — 20— 24 — 2 1 2 5 — 9 — 13 — 17 — 21 — 1 1 2 — 6 — 10 — 14 — 18 — 22 — 3 —7 — 11 — 15 — 19 — 23 — 4 — 8 — 12 — 16 — 20 — 24 — 3 1 — 5 — 9 — 13 —17 — 21 — 2 2 2 1 6 — 10 — 14 — 18 — 22 — 3 — 7 — 11 — 15 — 19 — 23 — 4— 8 — 12 — 16 — 20 — 24 — 4 1 — 5 — 9 — 13 — 17 — 21 — 2 2 2 2 6 — 10 —14 — 18 — 22 — 3 — 7 — 11 — 15 — 19 — 23 — 4 — 8 — 12 — 16 — 20 — 24 — 51 — 5 — 9 — 13 — 17 — 21 — 3 3 2 — 6 — 10 — 14 — 18 — 22 — 3 1 7 — 11 —15 — 19 — 23 — 4 — 8 — 12 — 16 — 20 — 24 — . . .

Here, representations would be offered at the server and advertised inthe MPD for download, each of which relates to one tile 50, i.e. onesection of the scene. Representations relating to one tile 50, butencoding this tile 50 at different qualities would be summarized inadaptation set which grouping is optional, but exactly this grouping isused for association to buffers. Thus, according to this example, therewould be one buffer per tile 50, or in other words, per viewport (viewsection) encoding.

Another representation set and distribution would be

R T Q T Q T Q T Q T Q T Q A buffer 1 1 1 5 1 9 2 13 2 17 2 21 2 1 1 2 16 2 10 1 14 1 18 1 22 2 3 1 7 2 11 2 15 2 19 1 23 2 4 1 8 1 12 1 16 1 202 24 2 2 1 2 5 2 9 3 13 3 17 3 21 3 1 1 2 2 6 3 10 2 14 2 18 2 22 3 3 27 3 11 3 15 3 19 2 23 3 4 2 8 2 12 2 16 2 20 3 24 3 3 1 2 5 2 9 1 13 217 2 21 2 2 2 2 2 6 2 10 1 14 2 18 2 22 2 3 1 7 1 11 1 15 2 19 1 23 1 41 8 1 12 1 16 2 20 1 24 1 4 1 3 5 3 9 2 13 3 17 3 21 3 2 2 2 3 6 3 10 214 3 18 3 22 3 3 2 7 2 11 2 15 3 19 2 23 2 4 2 8 2 12 2 16 3 20 2 24 2 51 2 5 2 9 1 13 1 17 1 21 1 3 3 2 2 6 1 10 2 14 2 18 2 22 1 3 2 7 1 11 115 1 19 2 23 1 4 2 8 2 12 2 16 2 20 1 24 1 . . .

According to this example, each representation would cover the wholeregion, but the high quality region would focus onto one hemisphere,while a lower quality is used for the other. Representations merelydiffering in the exact qualities spent in this manner, i.e. equaling inhigher quality hemisphere's location, would be collected in oneadaptation set and are, according to this characteristic, distributedonto the buffers, here exemplarily six.

Thus, the following description assumes that such distribution ontobuffers according to different viewport encodings, video sub-region suchas tiles, associated with AdaptationSets or the like is applied. FIG. 8c illustrates the buffer fullness levels over time for two separatebuffers, e.g. tile 1 and tile 2, in a tile based streaming scenario asit has been illustrated in the last but least table. Enabling a clientto report fullness level of all its buffers allows that a serviceoperator may correlate the data with other streaming parameters tounderstand Quality of Experience (QoE) impact of his service setup.

The advantage therefrom is that buffer fullness of multiple mediabuffers on client-side can be reported with a metric and be identifiedand associated to a type of buffer. The association types are forexample:

-   -   Tile    -   Viewport    -   Region    -   AdaptationSet    -   Representation    -   Low quality version of the whole content

One embodiment of this invention is given in Table 1 that defines ametric for reporting buffer level status events for each buffer withidentification and association.

TABLE 1 List of buffer levels Key Type Description ComponentBufferLevelsList List of component buffers Entry Object An entry for a singlecomponent BufferLevel bufferId Integer Identifier of the componentBufferLevel componentType Integer Component Identifier of the componentBufferLevel BufferLevel List List of component buffer occupancy levelmeasurements during playout at normal speed. Entry Object One componentbuffer level measurement. t Real-Time Time of the measurement of thebuffer level. level Integer Level of the buffer in milliseconds.Indicates the playout duration for which media data of all active mediacomponents is available starting from the current playout time.

A further embodiments using viewport depending encodings is as follows:

In a viewport-dependent streaming scenario, a DASH client downloads andprebuffers several media segments related to a certain viewingorientation (viewport). If the amount of prebuffered content is toohigh, and the client changes its viewing orientation, the portion of theprebuffered content to be played out after the viewport change is notpresented and the respective media buffer is purged. This scenario isdepicted in FIG. 8 d

Another embodiment would relate to a traditional video streamingscenario with multiple representation (quality/bitrates) of the samecontent and maybe spatially uniform quality at which the video contentis encoded.

The distribution could then look like:

R T Q T Q T Q T Q T Q T Q A buffer 1 1 1 5 1 9 1 13 1 17 1 21 1 1 1 2 16 1 10 1 14 1 18 1 22 1 3 1 7 1 11 1 15 1 19 1 23 1 4 1 8 1 12 1 16 1 201 24 1 2 1 2 5 2 9 2 13 2 17 2 21 2 1 2 2 2 6 2 10 2 14 2 18 2 22 2 3 27 2 11 2 15 2 19 2 23 2 4 2 8 2 12 2 16 2 20 2 24 2 3 1 3 5 3 9 3 13 317 3 21 3 1 3 2 3 6 3 10 3 14 3 18 3 22 3 3 3 7 3 11 3 15 3 19 3 23 3 43 8 3 12 3 16 3 20 3 24 3 . . .

That is, here, each representation would cover the whole scene forinstance which may not be a panoramic 360 scene, but at differentquality, namely a spatially uniform quality, and these representationswould be distributed onto the buffers individually. All the examples setout in the last three tables should be treated as not limiting themanner at which segments 58 of representations offered at the server aredistributed onto the buffers. Different ways exist and the rule may bebased on membership of segments 58 to representations, membership ofsegments 58 to adaptation sets, the direction of locally increasedquality of a spatially unequally coding of the scene into therepresentation which the respective segment belongs to, the quality atwhich a scene is encoded into the respective segment belongs to and soforth.

A client could maintain a buffer per representation and, uponexperiencing a rise in available throughput, decide to purge theremaining low-quality/bitrate media buffer before playback and downloadhigh quality media segments of time durations within the alreadyexisting low-quality/bitrate buffer. Similar embodiments can beconstructed for streaming based on tiles and viewport dependentencodings.

A service operator may be interested in understanding what amount andwhich data was downloaded without being presented as this introducescost without gain on server-side and decreases quality on client side.Therefore, the invention is to provide a reporting metric thatcorrelates the two events ‘media download’ and ‘media presentation’ tobe easily interpreted. This invention avoids that verbosely reportedinformation about each and every media segment download and playbackstatus is to be analysed and allows efficient reporting of purgingevents only. The invention also includes identification of the bufferand association to the type as above. An embodiment of the invention isgiven in Table 2.

TABLE 2 List of purging Events Key Type DescriptionComponentBufferPurging List List of Component buffer purgingmeasurements Entry Object One Component buffer purging measurementbufferId Integer Identifier of the component BufferLevel componentTypeInteger Component Identifier of the component BufferLevel T Real-TimeTime of the measurement of the Component buffer purging. D IntegerMeasurement of the Component buffer purging duration in milliseconds.

FIG. 9 shows a further embodiment of how to implement advantageouslydevice 40, Device 40 of FIG. 9 may correspond to any of the examples setout above with respect to FIGS. 1 to 8 . That is, it may possiblycomprise a lock messenger as discussed above with respect to FIG. 8 abut does not have to and may use information 68 as discussed above withrespect to FIGS. 2 and 3 or information 74 as discussed above withrespect to FIGS. 5 to 7 c but does not have. Differing from thedescription of FIGS. 2 to 8 , however, with respect to FIG. 9 it isassumed that the tile-based streaming approach is really applied. Thatis, the scene content 30 is offered at server 20 in the tile-basedmanner discussed as an option above with respect to FIGS. 2 to 8 .

Although the internal structure of device 40 may differ from the onedepicted in FIG. 9 , device 40 is exemplarily shown to comprise selector56 and retriever 60 already discussed above with respect to FIGS. 2 to 8and, optionally, deriver 66. Additionally, however, device 40 comprisesa media presentation description analyzer 90 and a matcher 92. The MPDanalyzer 90 is for deriving from the media presentation descriptionobtained from server 20: at least one version at which thetemporally-varying spatial scene 30 is offered for the tile-basedstreaming, and to, for each of the at least one version, an indicationof benefitting requirements for benefitting from the tile-basedstreaming the respective version of the temporally-varying spatialscene. The meaning of “version” will become clear from the followingdescription. In particular, matcher 92 matches the benefittingrequirements thus obtained with a device capability of device 40 oranother device interacting with device 40 such as decoding capabilitiesof the one or more decoders 42, the number of decoders 42 or the like.The background or thoughts underlying the concept of FIG. 9 is thefollowing. Imagine, the tile-based approach uses, assuming a certainsize of view section 28, a certain number of tiles being comprised bysection 62. Further, it may be assumed that the media segments belongingto a certain tile form one media stream or video stream which is to bedecoded by a separate decoding instantiation, separate from decodingmedia segments belonging to another tile. Accordingly, the movingaggregation of a certain number of tiles within section 62 for which thecorresponding media segments are selected by selector 56, uses a certaindecoding capability such as the existence of respective decodingresources in the form of, for example, the corresponding number ofdecoding instantiations, i.e. the corresponding number of decoders 42.If such a number of decoders is not present, the service provided byserver 20 may not be useful for the client. Accordingly, the MPDprovided by server 20 may indicate the “benefitting requirement”,namely, the number of decoders needed to use the service provided.Server 20 may, however, provide the MPD for different versions. That is,different MPDs for different versions may be available by server 20 orthe MPDs provided by server 20 may, internally, be structured so as todifferentiate between different versions at which the service may beused. For instance, the versions could differ in field of view, i.e. thesize of view section 28. Difference sizes of field of view manifestthemselves in a different number of tiles within section 62 and may thusdiffer in the benefitting requirements in that, for instance, adifferent number of decoders may be needed for these versions. Otherexamples are imaginable as well. For example, while versions differingin field of view may involve the same plurality of media segments 46, inaccordance with another example, different versions at which scene 30 isoffered for tile-streaming at server 20 may differ in even thepluralities 46 of media segments involved in accordance with thecorresponding version. For example, the tile-partitioning in accordancewith one version is coarser that compared to the tile-hyphenpartitioning of the scene in accordance with another version, therebyusing a lower number of decoders, for instance.

Matcher 92 matches the benefitting requirements and thus, selects acorresponding version or rejects all versions, completely.

The benefitting requirements may, however, additionally concernprofiles/levels which the one or more decoders 42 have to be able tocope with. For example, a DASH MPD includes multiple positions thatallow for indicating profiles. Typical profiles describe attributes,elements that can be present at the MPD, as well as video or audioprofiles of the streams that are offered for each representation.

Further examples for the benefiting requirements concern, for example,the client's side capability to move the viewport 28 across the scene.The benefiting requirements may indicate a used viewport speed whichshould be available for the user to move the viewport so to be able toreally enjoy the offered scene content. The matcher would check, forinstance, whether this requirement is met be the, for example,plugged-in user input device such as HMD 26. Alternatively, a set of“sufficient types of input devices” could be indicated by way of thebenefiting requirements assuming that different types of input devicesfor moving a viewport are associated with typical movement speeds inorientation sense.

In a tiled streaming service of spherical video, there are too manyconfiguration parameters that can be dynamically set, e.g. number ofqualities, number of tiles. In a case where tiles are independentbitstreams that need to be decoded by separate decoders, if the numberof tiles is too high, it might be impossible for hardware devices withfew decoders to decode all bitstreams simultaneously. A possibility isto leave this as a degree of freedom and that a DASH device parses allpossible representations and counts how many decoders are used to decodeall the representations or a given number that cover the FoV of thedevices and thus derives whether it is possible or not for that DASHclient to consume the content. However, a more clever solution forinteroperability and capability negotiations is to use signaling in theMPD that is mapped to a kind of profile that is used as a promise to theclient that if a profile is supported, the offered VR content can beconsumed. Such a signaling should be done in the form of a URN, such asurn::dash-mpeg::vr::2016, which can be packed either at the MPD level orat adaptation sets. This profiling would mean that N decoders at Xprofile are enough for consuming the content. Depending on the profilesthe DASH client could ignore or accept an MPD or a part of an MPD(adaptation set). In addition, there are several mechanisms that do notinclude all information such as Xlink or MPD chaining, where fewsignaling for selection are made available. In such a circumstance theDASH client would not be able to derive whether it can consume thecontent or not. Exposing the decoding capabilities in terms of number ofdecoders and profile/level of each decoder by means of such an urn (orsomething similar) is used, such that the DASH client can now, whetherperforming Xlink or MPD Chaining or a similar mechanism, makes sense.The signaling could also mean different operation points such as Ndecoders with X profile/level or Z decoders with Y profile/level.

FIG. 10 further illustrates that any of the above described embodimentsand descriptions presented with respect to FIGS. 1 to 9 for client,device 40, server and so forth, may be expanded to the extent that theoffered service is expanded to the extent that the temporally-varyingspatial scene does not only vary in time, but also depending on anotherparameter. FIG. 10 , for instance, illustrates a variant of FIG. 1 wherethe available plurality of media segments resulting on the serverdescribe the scene content 30 for different positions of the view center100. In the schematic shown in FIG. 10 , the scene center is depicted tomerely vary along one direction X but it is obvious that the view centermay be varied along more than one spatial direction such astwo-dimensionally or three-dimensionally. This corresponds to a changeof the user in user position in a certain virtual environment, forexample. Depending on the user position in the virtual environment, itsavailable view changes and accordingly, scene 30 changes. Accordingly,in addition to the media segments describing scene 30 subdivided intotiles and temporal segments as well as different qualities, furthermedia segments describe a different content of scene 30 for a differentposition of the scene center 100. Device 40, or selector 56,respectively, would compute, depending on view section position and theat least one parameter such as parameter X, the addresses of mediasegments out of plurality 46 which are to be retrieved within theselection process and these media segments would then be retrieved fromthe server using the computed addresses. To this end, the mediapresentation description may describe a function depending on tileindex, quality index, scene center position as well as time t andresults in the corresponding address of the respective media segment.Thus, in accordance with the embodiment of FIG. 10 , the mediapresentation description would comprise such a computation rule whichdepends, in addition to the parameters set forth above with respect toFIGS. 1 to 9 , on one or more additional parameters. The parameter X maybe quantized onto any of levels for which respective scenerepresentations are coded by way of corresponding media segments withinplurality 46 in server 20.

As an alternative, X may be a parameter defining a view depth, i.e. adistance from the scene center 100 in radial sense. While offering scenein different versions differing in view center portion X allows for theuser “walking” through the scene, offering scene in different versionsdiffering in view depth would allow for the user “radially zoom” backand forth through the scene.

For multiple, non-concentrical viewports the MPD thus may use a furthersignaling of the position of the current viewport. Signaling can be doneon segment, representation or period level, or the like.

Non-concentric spheres: in order for a user to move, the spatialrelationship of the different spheres should be signaled in the MPD.This could be done by means of coordinates (x,y,z) in arbitrary units inrelation to the sphere diameter. In addition, the diameter of a sphereshould be indicated for each sphere. A sphere could be “good-enough” tobe used for a user that is in its center plus an additional space forwhich the content would be ok. If a user would move beyond that signaleddiameter, another sphere should be used for showing the content.

Exemplary signaling of viewport could be done relative to a predefinedcenter point in space. Each viewport is signaled relative to that centerpoint. In MPEG-DASH, this can be signaled e.g. in the AdaptationSetelement.

Element or Attribute Name Use Description AdaptationSet Adaptation Setdescription ViewPortPosition 0...1 Describes the relative distance toViewportcenter Legend: For attributes: M = Mandatory, O = Optional, OD =Optional with Default Value, CM = Conditionally Mandatory, F = Fixed.For elements: <minOccurs> ... <maxOccurs> (N = unbounded) Note that theconditions only holds without using xlink:href. If linking is used, thenall attributes are “optional” and <minOccurs = 0> Elements are bold;attributes are non-bold and preceded with an @, List of elements andattributes is in italics bold referring to those taken from the Basetype that has been extended by this type.

Element or Attribute Name Use Description ViewPortPosition Viewportposition description @viewport_x M Distance of sphere center pointexpressing the horizontal distance to the global center with coordiantesx = 0, y = 0, z = 0. @viewport_y M Distance of sphere center pointexpressing the vertical distance to the global center with coordiantes x= 0, y = 0, z = 0. @viewport_z M Distance of sphere center pointexpressing the depth (z) distance to the global center with coordiantesx = 0, y = 0, z = 0. @viewport_diameter M Diameter of the sphere Legend:For attributes: M = Mandatory, O = Optional, OD = Optional with DefaultValue, CM = Conditionally Mandatory, F = Fixed. For elements:<minOccurs> ... <maxOccurs> (N = unbounded) Note that the conditionsonly holds without using xlink:href. If linking is used, then allattributes are “optional” and <minOccurs = 0> Elements are bold;attributes are non-bold and preceded with an @, List of elements andattributes is in italics bold referring to those taken from the Basetype that has been extended by this type.

Lastly, FIG. 11 illustrates that information such as or similar to thatdescribed above with respect to reference number 74 may reside in avideo bit stream 110 into which a video 112 is encoded. A decoder 114decoding such a video 110 may use information 74 to determine a size ofa focus area 116 within video 112 onto which a decoding power fordecoding video 110 should be focused. Information 74 could, forinstance, be conveyed within an SEI message of video bit stream 110. Forexample, the focus area could be decoded exclusively, or decoder 114could be configured to start decoding each picture of the video at thefocus area, instead of, for example, the upper left picture corner,and/or decoder 114 could cease decoding each picture of the video uponhaving decoded the focus area 116. Additionally or alternatively, theinformation 74 may be present in the data stream simply for beingforwarded to a subsequent renderer or a viewport control or thestreaming apparatus of client or segments selector for deciding whichsegments to download or stream in order to cover which spatial sectionat all or at increased or predetermined quality. The information 74indicate, for example, as outlined above, a recommended area as arecommendation to place the view section 62 or section 66 to coincidewith, or cover, or track, this area. It may be used by the client'ssegment selector. Just as it was true with respect to the descriptionwith respect to FIG. 4 to 7 c, information 74 may set the dimension ofarea 116 absolutely, such as in number of tiles, or may a set a speed ofarea 116 wherein the area is moved, for example, according to userinput, or the like, in order to follow a interesting content of thevideo spatiotemporally, thereby scaling area 116 so as to increase withincreasing indication of the speed.

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus. Some or all of the method steps may be executed by (or using)a hardware apparatus, like for example, a microprocessor, a programmablecomputer or an electronic circuit. In some embodiments, one or more ofthe most important method steps may be executed by such an apparatus.

The signals occurring above such as the streamed signal, the MPD or anyother of the mentioned signals can be stored on a digital storage mediumor can be transmitted on a transmission medium such as a wirelesstransmission medium or a wired transmission medium such as the Internet.

Depending on certain implementation requirements, embodiments of theinvention can be implemented in hardware or in software. Theimplementation can be performed using a digital storage medium, forexample a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM,an EEPROM or a FLASH memory, having electronically readable controlsignals stored thereon, which cooperate (or are capable of cooperating)with a programmable computer system such that the respective method isperformed. Therefore, the digital storage medium may be computerreadable.

Some embodiments according to the invention comprise a data carrierhaving electronically readable control signals, which are capable ofcooperating with a programmable computer system, such that one of themethods described herein is performed.

Generally, embodiments of the present invention can be implemented as acomputer program product with a program code, the program code beingoperative for performing one of the methods when the computer programproduct runs on a computer. The program code may for example be storedon a machine readable carrier.

Other embodiments comprise the computer program for performing one ofthe methods described herein, stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, acomputer program having a program code for performing one of the methodsdescribed herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a datacarrier (or a digital storage medium, or a computer-readable medium)comprising, recorded thereon, the computer program for performing one ofthe methods described herein. The data carrier, the digital storagemedium or the recorded medium are typically tangible and/ornon-transitionary.

A further embodiment of the inventive method is, therefore, a datastream or a sequence of signals representing the computer program forperforming one of the methods described herein. The data stream or thesequence of signals may for example be configured to be transferred viaa data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example acomputer, or a programmable logic device, configured to or adapted toperform one of the methods described herein.

A further embodiment comprises a computer having installed thereon thecomputer program for performing one of the methods described herein.

A further embodiment according to the invention comprises an apparatusor a system configured to transfer (for example, electronically oroptically) a computer program for performing one of the methodsdescribed herein to a receiver. The receiver may, for example, be acomputer, a mobile device, a memory device or the like. The apparatus orsystem may, for example, comprise a file server for transferring thecomputer program to the receiver.

In some embodiments, a programmable logic device (for example a fieldprogrammable gate array) may be used to perform some or all of thefunctionalities of the methods described herein. In some embodiments, afield programmable gate array may cooperate with a microprocessor inorder to perform one of the methods described herein. Generally, themethods may be performed by any hardware apparatus.

The apparatus described herein may be implemented using a hardwareapparatus, or using a computer, or using a combination of a hardwareapparatus and a computer.

The apparatus described herein, or any components of the apparatusdescribed herein, may be implemented at least partially in hardwareand/or in software.

The methods described herein may be performed using a hardwareapparatus, or using a computer, or using a combination of a hardwareapparatus and a computer.

The methods described herein, or any components of the apparatusdescribed herein, may be performed at least partially by hardware and/orby software.

While this invention has been described in terms of several embodiments,there are alterations, permutations, and equivalents which will beapparent to others skilled in the art and which fall within the scope ofthis invention. It should also be noted that there are many alternativeways of implementing the methods and compositions of the presentinvention. It is therefore intended that the following appended claimsbe interpreted as including all such alterations, permutations, andequivalents as fall within the true spirit and scope of the presentinvention.

REFERENCES

-   [A1] ISO/IEC 23009-1:2014, Information technology—Dynamic adaptive    streaming over HTTP (DASH)—Part 1: Media presentation description    and segment formats

What is claimed is:
 1. A method for encoding an omni-directional orspherical video into a video bitstream, wherein the omni-directional orspherical video shows a spatial scene and the video bitstream has theomni-directional or spherical video encoded thereinto in a manneraccording to which the spatial scene is mapped onto pictures of theomni-directional or spherical video using a cubic projection, the methodcomprising: providing SEI messages of the video bitstream with asignalization associated with multiple recommended viewport sections ofthe omni-directional or spherical video determined based on ameasurement of a statistical value, wherein the signalization indicatesthat the multiple recommended viewport sections are organized as a listranked according to a frequency ranking gained by statistics of userpopularity, and an indication of a temporal persistence of thesignalization, wherein the SEI messages of the video bitstream providefor the signalization in a manner so that the multiple recommendedviewport sections are variable spatiotemporally across theomni-directional or spherical video.
 2. The method of claim 1, whereinthe signalization indicates a size and a position of the multiplerecommended viewport sections in a manner differentiating betweendifferent ways of controlling a movement of the multiple recommendedviewport sections.
 3. The method of claim 2, wherein the different waysdifferentiate between at least two of view section control by headmovement, eye movement and tablet movement.